Warning that flu symptoms are changing as US already suffering worst season in 25 years: ‘We’re really worried what’s to come’

Last year was the deadliest flu season for kids since CDC record-collecting began 20 years ago

As cases of flu have reached their highest level in 25 years in the U.S., doctors are warning Americans that symptoms of this year’s strain are different from those seen in previous years.

For one, there has been more incidence of long-lasting fever than is typical, Dr. Mark Loafman, the chair of Family and Community Medicine at Cook County Health, told NBC Chicago.

"More fever with the flu this year than people are accustomed to,” he said. “And the fever can last up to seven days, so five to seven days. And that's worrisome.”

And, there are more gastrointestinal-related issues in adults, Loafman said. Usually, vomiting is seen more in pediatric flu cases.

Dr. Juanita Mora, the national spokesperson for the American Lung Association, also told the station that some cases aren’t responding to long-relied-on medications, such as Tylenol or Motrin.

Cases of flu are surging across the U.S. – along with different symptoms than previous years (Getty)

"This new strain has symptoms of really high fevers. It has a really bad cough that won't go away, very phlegmy, and also vomiting and diarrhea and lots of joint aches as well as muscle aches," Mora said.

Of course, infection still involves other typical symptoms, such as a cough, sore throat, stuffy nose, body aches and fatigue.

Symptoms typically start within one and four days of exposure, according to the U.S. Centers for Disease Control and Prevention.

The combination of these factors, more severe infections in older adults and expert concerns that this year’s flu vaccine doesn’t perfectly match the virus may have contributed to landing 30 states in the CDC’s worst tier for flu activity before the end of the season’s peak.

"The fact that we've seen steady increases over the last several weeks without much of a decline or even a flattening would suggest to me that we've got the peak ahead of us," Dr. Robert Hopkins, medical director of the National Foundation for Infectious Diseases, told The Associated Press.

Child flu deaths tick up after a record season

To date, there have been at least 11 million illnesses, 120,000 hospitalizations and some 5,000 deaths.

The nation is at the highest level of respiratory illness since the 1997-1998 flu season, according to federal data.

“This is definitely a banner year,” epidemiologist Dr. Caitlin Rivers told CNN. “It’s the worst we’ve had in at least 20 years. We’re seeing a majority of the country is experiencing very high levels of activity, and we’re still in the thick of it.”

This comes on the heels of the worst flu season in 15 years last year, and the deadliest flu season for kids since the CDC started collecting flu data 20 years ago.

There have been nine pediatric deaths reported by the CDC so far this season, although Illinois just reported its first child flu death on Monday and it’s unclear if that death was included in the national tally.

The news came the same day as federal health officials announced they would no longer recommend flu vaccinations for children.

It’s not too late to get your flu shot, experts say (AP)

People ages 65 and older, pregnant women, young children and people who have any chronic health problems are at an increased risk for infection.

“In my practice alone, we’ve hospitalized several kids over the past few weeks, and it’s just starting, so we’re really worried about what’s to come,” Dr. Eric Ball, a pediatrician based in California’s Orange County, told SFGate.

Is it too late to get a flu shot?

While current flu vaccines don’t fully cover the new variant, experts stress getting the shot is still the best way to prevent the most severe effects of infection.

“It’s not too late to get a flu shot, which health experts say can still prevent severe illness even if someone gets infected,” the American Red Cross said in a statement.

“According to the CDC, only about 42 percent of adults and children have gotten a flu vaccination so far this year.”